1. Field of the Invention
This invention relates generally to photographic printing apparatus and more particularly, to photographic printing apparatus intended to handle film, either negatives or transparencies wherein the edges of the film are supported in a mount such as a slide frame or aperture-type masking card.
2. Description of the Prior Art
A major problem encountered in the field of photographic printing is the difficulty in maintaining sharp focus of an image mounted in a frame, such as a slide. One cause of loss of focus is due to the tendency of the photographic material to curl, with the concave side of the curl being on the emulsion side of the photographic material.
Various devices have been used in the prior art to solve this problem. One proposed solution is disclosed in U.S. Pat. No. 3,397,613, issued to K. J. Kallenberg. It is a device for supporting a single photographic transparency mounted in a frame and includes a lower transparent holder formed of a base portion having a table portion extending upwardly from the base portion. The table portion has a flat upper surface having an area less than that of the base portion, such that it can fit within the recess formed in the aperture of the slide mount. An upper mount has a similar shape and fits into the recess in the slide mount above the transparency. Thus, the transparency is held between the upper and lower table portions independent of the slide mount.
Several difficulties exist with respect to such prior art devices. Because most commercial photographic printers must be capable of handling multiple film formats, it is necessary that a different transparency holder be provided for each film format that the printer accommodates.
Because of the discontinuities in height presented by the transparency holder, it makes it difficult for both the manual and automatic placement of the mount onto the holder. Any excessive sliding of the mount on the holder in an effort to position the table portion of the plate in the mount aperture would result in the scratching of the film by the upwardly extending table portion.